This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2002-72017 filed in Korea on Nov. 19, 2002, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a method of forming a patterned film of carbon nanotubes via a photolithography process by using surface-modified carbon nanotubes, whereby double-bond-containing functional groups are introduced into the surfaces of the carbon nanotubes. More specifically, the present invention relates to a method of forming a negative pattern of carbon nanotubes by modifying carbon nanotubes by introducing double bond-containing functional groups that can go through radical polymerization into the surfaces of the carbon nanotubes; coating a substrate with a liquid coating composition prepared by dispersing the surface-modified carbon nanotubes in an organic solvent along with a photoinitiator; exposing the film to UV light through a photomask to induce photo-polymerization of the double bond on the surface of the carbon nanotubes; and developing the film.
2. Related Art
Since carbon nanotubes were found by Dr. Iijima at Maijo University of Japan in 1991 while researching electro-microscopic observation, many studies of carbon nanotubes have been profoundly made. Typically, a carbon nanotube is a graphite sheet having a hollow cylinder structure with an inner diameter of 1 to 20 nm.
In graphite that has been known to have a peculiar structure, covalent bonds between carbon atoms are arranged in such an unusual style that graphite has the shape of a rigid, flat, hexagonal sheet. The upper and lower regions of the sheet are filled with dispersed free electrons that are maintaining their motion parallel to the sheet. In order to form carbon nanotubes, the graphite sheet is configured to be spirally wound and in this structure, edge bonds are formed at different sites. Generally, various electrical properties of the carbon nanotube are believed to be a function of its structure and diameter (Phys. Rev. (1992) B46:1804 and Phys. Rev. Lett. (1992) 68:1579). Thus, changing the spiral shape or chirality of the carbon nanotube results in a change in the free electrons motion, and, in terms of the free electrons' motion, the carbon nanotubes exhibit a conductivity from metallic material to a semiconductor. As a semiconductor, the range of the barrier voltage for free electrons to overcome varies with the tube's diameter and, in case of the smallest diameter, the voltage can be as low as 1 eV. In other words, it is possible for carbon nanotubes to have various electrical properties from those of insulator to those of semiconductors or metals, depending on the structure and diameter. In addition, not only do the carbon nanotubes show mechanical durability and chemical stability but they have a hollow cylindrical structure having a small diameter and a long length. Thanks to all these characteristics, the possible application fields of the carbon nanotubes becomes wider, including flat-panel displays (FPD), transistors, energy storing material and electronic devices of nano-size.
Recently, a method of arranging carbon nanotubes on a gold substrate was reported by Zhongfan Liu at Beijing University, the People's Republic of China, wherein every end of the carbon nanotube was modified with sulfur (Langmuir (2000) 16:3569). Another method was reported by Smalley at Rice University, U.S.A., wherein the method comprises the steps of: forming a self-assembled monolayer of trimethylsilyl groups on a silicone substrate; patterning the monolayer using electron beams; attaching amine groups to the pattern; and attaching carbon nanotubes to the amine groups (Chemical Physics Letters (1999) 303:125). However, this method is not thought to be advantageous because the self-assembled monolayer of trimethylsilyl groups is very unstable and susceptible to a change of surroundings.